Our long-term objective has been, and will continue to be, to better understand the mechanisms governing infection and disease by Salmonella when administered by the normal oral route of entry. We will study S. typhimurium infection of chicks to evaluate persistent intestinal colonization and mice as a model of typhoid fever in humans and will make extensive use of murine and human cells in culture. We will continue, in all our endeavors, to develop methods to identify and analyze mechanisms for regulated expression of genes that might contribute to pathogenicity. Specifically, we will: (1) evaluate expression of S. typhimurium genes at ambient temperatures in a simulated polluted water environment with the objective to identify genes enhancing survival and potentiating successful colonization of the warm-blooded animal host and, subsequently, to characterize their functions and means of regulation, (2) define roles of adhesins in targeting Salmonella to specific cell types and tissues in the murine host, in enabling long-term colonization of the intestine and cecum in chicks, and in contributing to surface colonization (biofilm formation) in the simulated polluted water medium at ambient temperatures, and (3) continue to define mechanisms for colonization of the GALT (Peyer's patches) by identification of expressed genes with subsequent generation of mutants for characterization and complementation and to establish the means of their regulation. In these studies, we will extensively employ newly developed molecular genetic tools, such as selective capture of transcribed sequences (SCOTS), an easy and efficient method to generate mutant strains with defined deletion mutations, and selective regimens to generate operon fusions in addition to more standard means of genetic and molecular genetic manipulation. Our studies will use a broad range of methods of microbial genetics, molecular biology, biochemistry, immunology, cell biology, microscopy and animal science. All experiments will be conducted under conditions that preclude infections of workers and inadvertent release of infectious microorganisms.